1. Field of the Invention
The present invention relates to improved ways and means to format the drive for a magnetic recording disk and, more particularly, to such ways and means which operate without sensors for sensing the location of the read/write transducer utilised in conjunction with the disk.
2. Description of the Prior Art
In the field of electronic computer technology, it is typical to store data in binary form on the face of a rotatable disk, which face is coated with a magnetizable substance such as iron oxide. In operation, such disks are rotated somewhat like phonograph records and the binary data is encoded upon, or retrieved from, the face of the disk by a movable magnetic transducer device called a read/write head. More particularly, the binary information is magnetically encoded on the face of the disk in concentric rings, called tracks, and the read/write transducer is selectively positioned in a direction radial of the disk to select a particular track at which information is to be recorded or retrieved.
On such magnetic recording disks, it is known to have track densities of about one thousand tracks per inch of the radius of the disk. Accordingly, precise positioning of a read/write head is necessary so that the head can accurately gain access to a particular desired track on the surface of the disk.
In conventional magnetic recording disk systems, a read/write transducer is driven to seek a desired track on the disk by means of a motor called a stepping motor coupled to a capstan mechanism. Such motors and capstan mechanisms translate electrical commands from a controller for the disk drive system to linear movement of the read/write transducer radially across the face of the magnetic recording disk. To accurately locate the read/write transducer on a desired track on a magnetic disk, it is necessary that the controller have precise information as to the location of the read/write head relative to the disk. To have such information, it is conventional for the controller to keep an account of the movements (i.e., radial steps) of the read/write head from some initial location, either at the inner or outer periphery of the disk. Thus, for example, if the read/write transducer were initially at the inner periphery of the disk (typically called the inner guard band) and moved thirty tracks radially outward of the disk, the controller would store such positioning information and, if it were necessary to subsequently move the read/write head a number of tracks radially inward of the disk, the controller would compute the radial steps required to reach new position based upon the information previously stored in the controller relating to prior movements of the read/write head. Accordingly, in conventional controller systems for read/write heads, it is necessary for the controller to precisely monitor and record each movement of the read/write head, so as to be aware of the location of the read/write head at any instant. Obviously, in such systems, it is critical to have exact information as to the starting point of the movement of the read/write head; in typical disk drive systems, the starting point of movement of the read/write head is known as "track-zero".
In prior art controller systems for disk drives utilizing an "open-loop" mode of operating control, it is conventional to provide a sensor device for sensing the track-zero location of the read/write head. Such a sensor device physically senses any contact with the read/write transducer or its positioning mechanism and transmits information relating to such contact to the disk drive controller. In practice, the track-zero sensor is carefully and precisely located during fabrication of the disk drive so that the read/write head can be exactly placed at the starting place of the data field on a magnetic recording disk. Precise location of the track-zero sensor in such prior art systems has been understood to be critical to reliability of the read/write function, not only insofar as locating the beginning of the data area on a magnetic recording disk but also for accurately locating any defect locations on the disk.
To format disk drive systems incorporating track-zero sensors, the read/write transducer is radially moved across the face of a magnetic recording disk until the track-zero sensing line is found. Then, after this information is transmitted to the controller unit by the track-zero sensor device, the controller unit operates the positioning mechanism for the read/write transducer such that the transducer incrementally steps from track-to-track across the disk to a desired location in the data area for the entry or reading of particular data.
It may be appreciated that a track-zero sensor is a critical and costly element in such prior art systems. Not only is there an initial cost to providing a track-zero sensor and its associated drivers and receivers to transmit information from the sensor to the controller, but there is a need for precise adjustment of the position of the track-zero sensor during the manufacturing of the disk drive assembly. As might be expected, there are also frequent needs to provide adjustment or maintenance of the track-zero sensors after the disk drive assemblies have been placed in actual usage.